As Sony Pictures struggles to recover from one blow after another related to the devastating cyber attack , one may overlook the fact that its parent company in Japan has been a popular target of hackers for years .

Three years ago , in April 2011 , Sony 's PlayStation network was shut down for nearly a month when hackers stole the personal information of an estimated 77 million people .

That same year , in June , hackers released 150,000 Sony Pictures records including usernames and passwords and claimed to have compromised the private information of more than one million people .

In October 2012 , hacker group `` The Three Musketeers '' released a security key that allowed PS3 users to run pirated games .

Despite those incidents , a group with suspected ties to North Korea calling itself `` Guardians of Peace '' was able to infiltrate Sony 's computer system , steal an incredible amount of data , and use it to launch the most vicious cyber-attack in history on an American corporation .

Former Sony employees are suing the company for failing to protect their privacy . Many are asking what lessons -- if any -- Sony learned from those previous hacks .

Asia Strategist Keith Henry says Sony was taken by complete surprise last month when the cyber-terrorists successfully stole massive amounts of data and used it to devastate the company .

`` They can inflict damage . Immense amount of damage to corporate America , '' Henry says .

They posted personal information like addresses and social security numbers , private emails that contained embarrassing revelations about top executives and Hollywood stars , insider information about the studio 's tactics , and they even posted five Sony movies on file-sharing websites .

Tokyo-based cyber security firm LAC is the only line of defense for about 850 clients . It has a confidential list of private companies and government agencies .

`` The hackers are always getting more advanced , '' says LAC Chief Technology Officer Itsuro Nishimoto .

And they are sometimes too far ahead of those trying to keep up . Nishimoto says a devastating hack like the one on Sony Pictures can penetrate even the best cyber-defense . He says the Sony network may be more vulnerable because of the large amount of users with varying degrees of access .

Sony appears to be trying to avoid further provoking North Korea , the prime hacking suspect , telling CNN simply `` the investigation is ongoing . ''

The Japanese government is also distancing itself . A spokesperson for the Ministry of Foreign Affairs tells CNN the hack is a `` United States issue . ''

Henry says the world is coming to terms with the new reality of cyber-terrorism .

`` One of the reasons nobody is willing to make a statement is because they do n't know what to say , '' Henry says .

Jeff Kingston , a professor of Asian Studies at Temple University in Tokyo says the attack reveals lax cyber-security among Sony 's ranks . But he suspects it is a more widespread problem in Japan .

`` I think this is a wake-up call for Japan that this is a problem . This is a huge vulnerability . And they 're not really managing this risk very well or very aggressively , '' Kingston said . `` It does suggest a certain level of corporate complacency . ''

Defector : North Korea has vast hacker network

5 lessons from the Sony hack

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Sony in Japan has been a popular target of hackers for years

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PlayStation network was shut down in April 2011 when hackers stole information of 77M people

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Former Sony employees are suing the company for failing to protect their privacy

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Analyst says attack reveals lax cyber-security among Sony 's ranks